1. Field of the Invention
The present invention relates to a copier, printer, facsimile apparatus, multifunction machine or similar image forming apparatus. More particularly, the present invention relates to a device for preventing toner from flying out of a developing device and an image forming apparatus using the same.
2. Description of the Background Art
An electrophotographic image forming apparatus, for example, includes a developing device for developing a latent image formed on an image carrier with toner to thereby form a corresponding toner image. The toner image is transferred from the image carrier to a sheet or recording medium. The problem with this type of apparatus is that toner not contributed to development flies out of the developing device via an opening and deposits on, e.g., the sheet, lowering image quality. In addition, such toner smears the operator""s hand in the event of maintenance.
Japanese Patent Laid-Open Publication No. 10-3220, for example, discloses a toner scatter preventing device including a filter case on which a fan and a filter are mounted. The fan sucks air out of a developing device via a hole formed in the developing device and discharges it, thereby preventing toner from flying out via the opening of the developing device. The filter collects toner entrained by the resulting air stream. The collected toner is stored in a tank.
The device taught in the above document has the following problems left unsolved. The toner collected by the filter accumulates on the filter and weakens the air stream, finally fully stopping up the filter. Further, the toner accumulated on the filter drops into the developing device in the form of large lumps and deposits on the image carrier. This makes the density of toner images irregular and thereby lowers image quality.
Particularly, when toner with a small grain size is used to meet the increasing demand for faithful reproduction of dots and tonality, the toner that is fine powder is apt to fly about in air. As a result, the air stream entraining the toner from the developing device increases the amount of toner collected by suction due to the small grain size, stopping up the filter or filling up the tank soon. Such toner therefore results in the need for frequent maintenance. It follows that maintenance cost increases although high image quality is achievable.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Publication No. 60-3188, Japanese Patent Laid-Open Publication Nos. 2000-284523 and 2001-92254, and Japanese Utility Model No. 2,527,797.
It is an object of the present invention to provide a toner scatter preventing device capable of preventing toner from scattering over a long period of time while insuring high image quality, and an image forming apparatus using the same.
It is another object of the present invention to provide a toner scatter preventing device capable of reducing the amount of toner to fly about and extending maintenance interval even when toner with a small grain size is used, and an image forming apparatus using the same.
A toner scatter preventing device of the present invention is applicable to an image forming apparatus of the type developing a latent image formed on an image carrier with toner stored in a developing device. The device includes an exhausting device for discharging air present in the developing device via an exhaust passage. A toner collecting device collects the toner entrained by air discharged by the exhausting device. A toner storing device is positioned upstream of the toner collecting device in the direction of air flow for storing the toner collected by the toner collecting device without causing it to drop into the toner present in the developing device. The developer is a toner and carrier mixture in which carrier grains have a weight mean grain size of 65 xcexcm or below.